Iliopsoas Muscle

Author: Scott A. Sheffield MS

Last update: May 25th, 2023

The iliopsoas is composed of two muscles: the iliacus and psoas major. Along with the psoas minor, these muscles form the group of inner hip muscles.

Located deep within the pelvic region, the iliopsoas muscle spans between the hip bone and femur, serving a variety of functions for the hip joint. This article will discuss the anatomy and functions of this muscle.

Iliacus muscle
Origin	Iliac fossa; Iliac crest.
Insertion	Lesser trochanter of the femur (via shared tendon with psoas major)
Innervation	Femoral nerve
Functions	Together with psoas major: Flexion and external rotation of the thigh;

Psoas major muscle
Origin	Transverse processes of lumbar vertebrae L1-L5; Bodies of T12-L5 and their intervertebral discs.
Insertion	Lesser trochanter of the femur (via shared tendon with iliacus)
Innervation	Anterior rami of lumbar spinal nerves L1-L3
Functions	Together with iliacus: Flexion and external rotation of the thigh; Contracting alone: Lateral flexion of the trunk

Origin and Insertion

The psoas major and iliacus muscles have distinct origins but share a joint insertion. The iliacus muscle originates from the iliac fossa and iliac crest. The psoas major originates from the transverse processes of lumbar vertebrae L1-L5 and some adjacent structures, including the bodies of T12-L5 vertebrae and the intervertebral discs between them.

Both muscles converge towards the femur, and via a shared tendon, they insert onto the lesser trochanter of the femur.

Innervation

The two components of the iliopsoas muscle have different innervations:

• Psoas major is innervated by the anterior rami of lumbar spinal nerves L1-L3
• Iliacus is innervated by the femoral nerve

Solidify your knowledge of the anatomy of the back muscles with more in-depth articles.

Functions

The iliopsoas muscle is the primary and .  When the insertion is the fixed point, the psoas major contributes to the flexion of the trunk during bilateral contraction (contraction from both sides). When only one psoas major contracts in this manner (unilateral contraction), it aids in the lateral flexion of the trunk.

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References

• Open Anatomy. (n.d.). TA2 Viewer. Retrieved April 5, 2023, from https://ta2viewer.openanatomy.org/
• Betts, J. G., Young, K. A., Wise, J. A., Johnson, E., Poe, B., & Kruse, D. H. (2022). Anatomy and Physiology (2nd ed.). OpenStax. https://openstax.org/details/books/anatomy-and-physiology-2e
• Palastanga, N., & Soames, R. (2012). Anatomy of Human Movement (6th ed.). Edinburgh, Scotland: Churchill Livingstone.
• Moore, K. L. (2018). Clinically Oriented Anatomy (8th ed.). Philadelphia, PA: Wolters Kluwer.
• Drake, R. L., Vogl, A. W., & Mitchell, A. W. M. (2015). Gray’s Anatomy for Students (3rd ed.). Edinburgh, Scotland: Churchill Livingstone.